1. Field of the Invention
The present invention relates to an ink jet printing apparatus, and more particularly to an ink jet printing apparatus provided with recovery operating means for a head which discharges the ink, and a head recovery method.
Also, this invention relates to an ink jet apparatus which can indicate the amount of ink remaining in an ink storing vessel by calculating the amount remaining based on the amount of ink discharged from the ink jet head and the amount of ink consumed by the recovery operation with said recovery operating means.
This invention is applicable to all ink jet printing apparatuses for forming an image on a printing medium, such as paper, cloth, leather, a nonwoven fabric, an OHP sheet, and a metal sheet, by discharging the ink. Specific examples of application devices may include business machines, such as a printer, a copying machine, or a facsimile terminal equipment, and industrial production equipment.
2. Related Backqround Art
Of the apparatuses which apply an ink jet system for discharging the ink, an ink jet recording apparatus (printing apparatus) for forming the image on the printing medium is well known.
Such an ink jet recording apparatus is provided with an ink jet recording head for discharging the ink to form the character or image on the recording medium such as paper by discharging the ink from the discharge ports provided in the ink jet recording head by driving discharge means.
The ink jet recording apparatuses can be classified into various different ink jet recording systems, according to the constitution of discharge means for discharging the ink. Typical examples of the ink jet recording system may include a system of discharging the ink by applying heat energy to the ink, using heat energy generating means such as electrothermal converting elements as discharging means, a system of discharging the ink by mechanically applying pressure to the ink, using electromechanical converting elements such as piezo-electric elements, etc. As the former, a so-called bubble jet system is well known in which using a discharging heater to apply heat energy to the ink to produce a bubble in the ink, particularly on the heater, the ink is discharged by using pressure generated when the bubble is produced (bubbling).
The ink jet recording apparatus has had a problem with the evaporation of the water content because the principal component of ink is its water content, or a problem that air bubbles may remain within the inside of discharge ports because the air enters through discharge ports, or the gas dissolved in the ink arises as air bubbles, degrading the discharge condition.
Also, in the above-mentioned bubble jet system, a discharging process includes repeatedly performing a step of producing the bubble by applying heat energy, and a step of enabling the bubble to shrink by stopping the application of heat energy. The ink jet recording apparatus of the bubble jet system has had a further problem that fine bubbles may remain in some of the ink flow passageways during the repetition of the above process, resulting in unstable ink discharge.
The ink jet recording apparatus is typically provided with various mechanisms for maintaining the quality of ink discharge by preventing the water content of the ink on or around the discharge ports where the ink is in contact with the air from evaporating to thicken the ink, or removing the thickened ink or produced bubbles.
In particular, the ink jet recording heads recently developed have the discharge ports or liquid channels communicating to them constructed extremely finely and at high density, and thereby are greatly influenced by the increased viscosity of the ink or unnecessary production of bubbles.
Therefore, the ink jet recording apparatus is provided with a capping mechanism for preventing the water content of ink evaporating from the discharge ports by enclosing (capping) the face where the discharge ports of the recording head are provided, when in the non-recording operation of discharging no ink droplets.
Also, to effect more stable ink discharging, it is known to perform various recovery operations to recover the discharge performance of the ink when starting the recording or periodically during the recording operation.
As one of the recovery operations, it is known to perform a discharge operation to expel the ink out of the discharge ports particularly not involving the recording by discharging the ink from all or desired discharge ports of the recording head at a predetermined position within the recording apparatus. By such a discharge operation not involving the recording, the ink is expelled out of the liquid channels in communication with the discharge ports that are employed less frequently in recording, and after exhaust, the new ink is supplied to replace (update) the ink within the liquid channels with the new ink having a normal viscosity. Such a discharge operation is referred to as a preliminary discharge operation because it occurs particularly when the recording is started.
Among other recovery operations, a recovery operation such as an ink suction operation or an ink pressure operation is well known in which with a mechanism for expelling the ink from the discharge ports, a suction operation or pressure operation is effected to expel the ink on or inside the discharge ports when starting the recording or at every desired time interval, thereby expelling the thickened ink and air bubbles together with the ink.
FIG. 1 shows the constitution of a main portion of a conventional ink jet recording apparatus.
In FIG. 1, 21 is an ink jet cartridge (hereinafter simply referred to as a "cartridge") to be mounted on a carriage 22, this cartridge integrally having a recording head (hereinafter simply referred to as a "head") having a nozzle section for jetting the ink, an ink tank as a vessel for storing the ink, and an ink supply unit having an ink supply passage. This cartridge 21 includes a Bk ink dedicated cartridge for recording only with the black ink (hereinafter abbreviating the black ink as Bk), and a color recording cartridge for recording with the color inks, these cartridges being replaceably mounted on the carriage 22 and selectively used. The carriage 22 and the cartridge 21 are electrically connected via a contact pad, not shown. 23 is an electrical substrate making up a control section for controlling the ink discharging by the cartridge 21, and 24 is a flexible cable for connecting its electrical substrate 23 to the carriage 22. 25 is a paper feed motor, whereby the recording sheet P is conveyed in a direction of the arrow f in the figure by the rollers 26, driven by this paper feed motor 25. Reference numeral 27 represents is rollers for forming the recording face for the cartridge 21 by regulating the recording sheet P flat in cooperation with the rollers 26. 28 is a carriage driving belt connected to the carriage 22, 29 is a motor for driving its belt in the directions of S in the figure, and 30 represents guide rails for the carriage 22. The carriage 22 can be moved in the directions of S along the guide rails 30, while being driven by the motor 29, to effect the recording on the recording surface.
Also, 31 is a recovery device as recovery means to effect the recovery operation as previously described for the head of the cartridge 21, opposed to the cartridge 21 at a home position H of the cartridge 21.
Also, the cartridge 21 mounted on the carriage 22 is driven in the directions of S in the figure over the recording sheet P by the motor 29, along with the carriage 22. The recording sheet P is conveyed in the direction of the arrow f as shown by the rollers 27, driven by the paper feed motor 25. Thereby, the secondary scanning by the recording head 21 is made. At this time, the recording head performs the recording on the recording sheet P by selectively jetting ink droplets under the control of a control unit.
In the recovery operation as previously described, the ink may be wastefully consumed if the recovery operation is made more than necessary, because the discharged ink is no longer usable for the recording. To avoid wasteful consumption of the ink to the utmost, it is desired to perform the recovery operation at the optimal timing. To this end, various control methods are taken, regarding the operation timing to effect the recovery operation, as well as the operation conditions. Among them, a method is especially effective of determining the operation timing based on the count value of a timer having a lower demand and backed up by a battery provided within a main body of the recording apparatus (hereinafter referred to as a "back-up timer control"). In particular, this back-up timer control is effective to construct a smaller recording apparatus with the ink consumption suppressed, because the power supply is frequently interrupted for the ink jet recording apparatus of the type which is small and portable for use.
Also, in the field of the ink jet printing, an ink jet unit having an ink jet head and an ink tank integrated (similar to the cartridge as previously described) has been recently employed from the aspects of smaller apparatus and easier maintenance by the user. This ink jet unit can be freely detachably mounted on the carriage in the printing apparatus, whereby the user can replace the ink jet unit with a new one when the ink within the ink tank is used up.
Moreover, with the increasingly higher demands of the color print, several constitutions which can meet the requirements of the coloration with the above ink jet unit have appeared, including, for example, those having arranged an ink jet unit for each color on the carriage to effect the color printing. Other constitutions may include those having freely detachably mounted on the carriage a color ink jet unit comprising as one component the ink tanks for storing the yellow, magenta and cyan inks individually for use in the color printing, and the ink heads for discharging these inks, and a unitary ink jet unit for the black ink alone.
Furthermore, a constitution has been proposed in which the ink jet head and the ink tank can be individually mounted freely detachably on the carriage.
The apparatuses which allow the user to mount or dismount the ink jet head and the ink tank on or from the apparatus, especially those which can mount only the black ink jet head and tank at certain times, and mount the other color heads and tanks at other times, in accordance with the image to be printed, had the following problems with controlling the recovery operation or managing the amount of ink remaining.
In the back-up timer control as previously described, control is enabled only for the head of the cartridge being currently mounted thereon, and for example, in an ink jet recording apparatus using a plurality of cartridges exchangeably, e.g., using exchangeably a monochrome cartridge for the Bk ink recording and a color cartridge for the color ink recording, while storing the unused cartridge within a special storage box, the back-up timer control was ineffective for the cartridge which was not mounted thereon. Therefore, in exchanging the cartridge, it is always necessary to stabilize the ink discharging by performing the recovery operation, with the result that there is an inconvenience that the ink will be consumed wastefully by that amount of discharge. That is, the conventional back-up timer control may result in the wasteful consumption of ink because the recovery operation may be conducted even when it is unnecessary. In the ink jet recording apparatus which is portable for use, it is required to reduce the capacity of the ink tank, according to the size of the apparatus, for the purposes of fabricating a smaller and lighter apparatus. However, the apparatus which has the wasteful consumption of ink will frequently result in no ink remaining if the smaller ink tank is used, requiring the ink tank to be frequently exchanged, with higher running costs. Accordingly, if the wasteful consumption of ink cannot be suppressed, the ink tank cannot be miniaturized, and the construction of a smaller recording apparatus is hampered.
Also, an ink jet recording apparatus is well known having the feature of informing the user of the ink remaining or that the ink is used up (hereinafter referred to as the ink remaining condition) by detecting or calculating the ink remaining within the vessel for storing the ink. Various methods for detecting the ink remaining have been proposed, but it is desirable to provide a mechanism capable of detecting more precisely the ink remaining or that the ink remaining has diminished.
To detect the ink remaining or the ink remaining condition correctly, it is desirable to take into consideration the amount of ink discharged by the recovery operation as previously described.
Conventionally, one example of ink remaining detecting means in the ink jet printing apparatus is well known, which is called a "dot count remaining detection". This method detects the ink remaining within the ink tank by measuring the amount of discharged ink or the amount of ink consumed in the recovery operation by counting the number of discharges or the number of recovery operations, and has the advantage that any special means for detecting the ink remaining is unnecessary, with the least cost.
The conventional examples with the above-mentioned dot count remaining detection were described in Japanese Patent Publication No. 5-19467, Japanese Patent Laid-Open Application No. 4-316856, and Japanese Patent Laid-Open Application No. 5-88552, for example. However, any dot count remaining detection described in these documents relies on counting the dots by considering that the quantity of ink droplets discharged from the head is constant. Also, the ink jet head in the printing apparatus is secured in any constitution. That is, the head is secured to the apparatus main body or the carriage movable along a predetermined area. If such a constitution is applied to the recording apparatus of the type using the cartridge having the ink jet head and the ink tank integrally, it only allows the use of one sort of cartridge, but is difficult to apply to the ink jet recording apparatus which employs a plurality of cartridges by exchanging them in accordance with the uses, as previously described.
By the way, the ink jet recording apparatus of the bubble jet system as previously described can discharge the ink by using electrothermal conversion elements or discharge heaters, heating the ink with the above heaters in accord with the discharge signal, and giving rise to film boiling in the ink to effect ink discharge by the bubbling force of a bubble produced thereby, but it has been found that the heat will be accumulated in the head due to the self-heating in discharging the ink or the outside air temperature condition, so that the ink temperature may change to cause varied volumes of ink to be discharged. Also, it has been found that in other ink jet systems, the amount of ink to be discharged may change owing to the effect of outside air temperatures.
The constitution of detecting the ink remaining by counting, supposing that the amount of discharged ink is constant, as in the conventional example as above described, may cause a relatively large detection error.
Also, the ink jet recording apparatus having exchangeably the ink jet unit employed in accordance with the purposes, e.g., printing in colors or black alone, had the problem in managing the ink remaining.
That is, if there are different kinds of inks to be discharged, the set amount of discharge for each head may vary, in which case, if the dot count remaining detection is directly conducted, the incorrect ink remaining detection may result. Also, if there are variations in the amount of discharge due to the effect of heat accumulation as above described, the ink remaining detection error will further increase.